With the rapid development of the positioning technology and the information technology, a Location-Based Service (LBS) has currently become an important part of the information services. When the outdoor positioning is mainly implemented by the Global Positioning System (GPS), the high-accuracy indoor positioning, as the positioning at the most detailed level, has accounted for an increasing proportion in the management of “digital city”. According to investigation, services regarding to positioning requirements and potential applications may bring marketing income of up to billions of dollars every year in the future, including a large number of indoor high-accuracy positioning requirements.
The current short-distance positioning is classified into a range-based positioning and a range-free positioning. Considering the positioning principles of the two types of position, the range-based positioning has a higher accuracy than that of the range-free positioning. At present, the range-based positioning has become a main research direction of the short-distance positioning. The range-based positioning is carried out mainly based on the measurement and estimation of the following parameters: Received Signal Strength Indication (RSSI), Time Of Arrival (TOA) which reflects the transmission time of a signal between nodes, Time Difference of Arrival (TDOA) which represents the difference of the transmission time of a signal from a tested node to two anchor nodes, and Angle Of Arrival (AOA) which represents the angle information between nodes.
The above-mentioned positioning technologies are specifically described below.
1) AOA technology: AOA estimation is to estimate AOA by measuring the received signal of each antenna array element in one antenna array via a multi-antenna technology (also called intelligent antenna technology), and then estimate the location of an unknown node according to the AOA. The AOA technology requires the condition of multiple antennas, i.e., the condition of an antenna array, and also has a higher requirement to the processing of a baseband signal, therefore, the implementation for both the hardware and the algorithm is very complex.
2) TOA technology: TOA estimation is to estimate the distance between a receiving antenna and a transmitting antenna according to the time of propagation of a signal transmitted by the transmitting antenna between the transmitting antenna and the receiving antenna. To estimate the propagation of a radio wave, especially the short-distance propagation of the radio wave, it is required that the receiving and the transmitting antennas should be in a very accurate synchronization relationship and the receiving antenna should have a very accurate clock, otherwise, a very small time difference may cause a very large distance error.
3) TDOA technology: TDOA estimation is to perform an estimation based on the difference of time when a radio wave transmitted by the transmitting antenna arrives at different receiving antennas and is developed from the TOA technology. Since the analyzed object is the time difference instead of absolute arrival time required by the TOA, the requirement on strict time synchronization in the TOA technology is reduced. However, the distance between the receiving antenna and the transmitting antenna is estimated according to a time parameter, therefore, the short-distance positioning still has a very high requirement to the accuracy of the clock of the receiving antenna.
4) RSSI technology: the RSSI technology is to estimate the distance between the receiving antenna and the transmitting antenna according to the RSSI received by the receiving antenna from the transmitting antenna mainly according to the principle that the RSSI and the distance are in an inverse proportion. The receiving antenna can extract the RSSI very easily, therefore, the RSSI technology is the most common short-distance positioning technology at present, but the technology has the defects of low accuracy and poor stability.
To solve the problem, there is still no effective solution yet.